I am having difficulty understanding the function of a Playback Sub.
I assumed that a Chase recorded to a Sub would loop, and a Playback recorded to a Sub would play once, but Playback also appears to loop through the steps.
Specifically I am trying to Pan/Tilt a moving head with the shutter closed in step 1 and then open the shutter in step 2.
Step 1 works fine and then step 2 opens the shutter but then the shutter closes / opens / closes / opens etc.

I've also tried the above using two standard channels and the same thing happens. The second step (channel) turns on and off repeatedly.